Ocean waves have been regarded as a potential source for energy extraction for over 200 years and many devices have been constructed to that end. However, all or almost all of the currently known devices fail to extract sufficient energy in an economic manner.
For example, many wave energy harvesters utilize alternating peaks and troughs of ocean waves to raise and lower part of the harvester to thereby extract mechanical energy from relative motions of at least two portions of the device. Motion of one portion of such devices is typically due to flotation on the rising and falling water surface as a wave passes the device which is in a relatively fixed position. Since the quantity of energy harvested is directly proportional to the weight of the device on the down stroke, or the buoyancy force on the upstroke, most known devices lag the wave. Typically, such devices sink as the water rises until relative buoyancy increases sufficiently to force the device upwards, and then emerge onto or above the water surface as the wave falls, since the downward stroke is used to extract energy from the device. As such devices are based on buoyant forces generated by the up-and-down motion of the wave, they are also known as point-absorbers.
For point absorbers which use buoyancy as the predominant actuating force, a float or other buoyant portion is tethered to a structure below the surface and the upward pull on the tether transmits the force that is harvested as energy. In some of these devices, the buoyant floats are attached to a fixed point via a flexible tether, and therefore are subject to tilting of the float upon forward force impingement of a wave. Moreover, due to the often V-shaped cross-section of the buoyant floats, the floats will typically submerge further than a comparably sized flat float.
In other known waver energy generators, the forward momentum of a wave is used exclusively. Such devices are commonly known as oscillating water column devices, in which the wave rushing into a cavity pushes air out of the cavity through a turbine. Alternatively, such devices allow a wave crest to rush into a cavity that is hydraulically coupled to one or more turbine. An exemplary device is described at the web address http://www.waveplane.com. Depending on the location, the forward momentum of a wave is substantial, and most clearly evidenced in breaking waves or waves used by surfers. While such wave energy harvesters are often mechanically more simple, various disadvantages remain. Among other things, only a portion of the wave energy is translated into harvested energy, and potentially usable energy from the up-and-down motion of the wave are typically lost.
In further known wave energy harvesters, hydrofoils are employed to transform at least part of the energy of a wave in a forward motion as described in WO 87/04401 to Cook, or U.S. Pat. Nos. 4,352,023 and 4,598,547 to Sachs et al and Danihel, respectively. While such devices achieve at least some advantage in their implementation, various disadvantages remain. Among other things, the force provided by the hydrofoils is typically used to align the wave energy system perpendicular to the wave, or to reduce water resistance, but not employed to generate energy.
Therefore, although numerous wave energy harvesters are known in the art, all or almost all of them suffer from one or more disadvantages. Consequently, there is still a need to provide improved configurations and devices for wave energy extraction.